1/(b+c)(c/b-b/c)+1/(a+c)(a/c-c/a)+1/(a+b)(b/a-a/b)=1/(b+c) × (c²-b²)/bc +1/(a+c) × (a²-c²)/ac +1/(a+b) × (b²-a²)/ab=(c-b)/bc + (a-c)/ac + (b-a)/ab=(ac-ab+ab-bc+bc-ac)/...